A substrate for semiconductor device is manufactured by forming deposit layers of a metal film working as a wiring and an interlayer insulating film on a silicon wafer substrate, subsequently conducting a surface planarization treatment by means of chemical mechanical polishing (hereinafter referred to as “CMP”) with an abrasive composed of an aqueous slurry containing fine abrasive particles, and then stacking new layers on the planarized surface. In microfabrication of a substrate for semiconductor device, each layer is required to have planarity with high precision, and importance of the planarization treatment by means of CMP becomes more and more high.
In a manufacturing step of a semiconductor device in recent years, a wiring (Cu wiring) composed of a cupper (Cu) film having a low value of resistance is introduced for the purpose of attaining increases in speed and integration degree in the device.
Although Cu is suited for microfabrication because of good workability, in view of the fact that Cu is easily oxidized and degraded in water and is easily corroded with acid components or alkali components, oxidation or corrosion of the Cu wiring is problematic in the CMP step.
For that reason, in CMP of a substrate for semiconductor device having a Cu wiring, an anticorrosive such as benzotriazole, tolyltriazole, or a derivative thereof, etc. is added to the abrasive, and this anticorrosive strongly adsorbs on the Cu surface to form a protective film, thereby suppressing the corrosion of the Cu wiring in CMP.
Large quantities of abrasive particles used in the CMP step, such as colloidal silica, etc., an anticorrosive-derived organic residue contained in the slurry, and the like are present on the surface of the substrate for semiconductor device after the CMP step, and therefore, in order to remove them, the substrate for semiconductor device after the CMP step is subjected to a cleaning step.
In cleaning after the CMP step, an acidic cleaning liquid and an alkaline cleaning liquid are used. In the acidic aqueous solution, the colloidal silica is positively charged, the substrate surface is negatively charged, and an electric attractive force acts, so that it becomes difficult to remove the colloidal silica. Meanwhile, in the alkaline aqueous solution, since abundant Off is present, both the colloidal silica and the substrate surface are negatively charged, and an electric repulsive force acts, so that it becomes easy to remove the colloidal silica.
In addition, in the acidic aqueous solution, Cu is oxidized into Cu2+ and dissolved in the liquid, whereas in the alkaline aqueous solution, Cu forms a passive film such as Cu2O or CuO on a surface thereof. For this reason, as compared with the acidic cleaning liquid, when the alkaline cleaning liquid is used, the corrosion in the cleaning step can be decreased. From these facts, it may be said that the alkaline cleaning liquid is advantageous in cleaning a fine Cu wiring.
A surfactant is used as one of constituent components of this cleaning liquid. The surfactant plays an important role for enhancing an affinity of the cleaning liquid with a substrate surface which is subjective to cleaning. By enhancing the affinity of the cleaning liquid to the substrate surface due to the surfactant added in the cleaning liquid, it is also possible to enhance a cleaning performance which the cleaning liquid has.
Patent Documents 1 and 2 describe an acidic cleaning liquid of a substrate for electronic material containing, as a main component, an organic acid. However, as described above, in view of the fact that in the acidic aqueous solution, surfaces of abrasive particles used in the CMP step, such as colloidal silica, etc., are charged with a positive charge, whereas a surface of a substrate for electronic material is charged with a negative charge, an electric attractive force acts therebetween, and therefore, it is difficult to remove such fine particles by using an acidic cleaning liquid.
Meanwhile, Patent Document 3 discloses an acidic cleaning liquid of a substrate for semiconductor device containing an anionic surfactant. Here, in order to control the charge on a fine particle surface in an acidic aqueous solution, the anionic surfactant is utilized. However, as described above, since a large quantity of an OH− ion is present in an alkaline liquid, from the standpoint of controlling the charge on the fine particle surface, it is clear that use of an alkaline cleaning liquid is more advantageous than use of an acidic cleaning liquid.
Patent Document 4 describes a cleaning liquid for cleaning an electronic circuit substrate, which contains tetramethylammonium hydroxide, monoethanolamine, and ascorbic acid. Since this cleaning liquid is an alkaline cleaning liquid, it may be expected that removal properties of fine particles are good. However, the monoethanolamine is high in corrosiveness against Cu, and in electronic circuits in which integration is advanced, corrosion thereof becomes a fatal defect, so that there is room for improvement.
In addition, although a KOH aqueous solution is preferable as the alkaline cleaning liquid because it is inexpensive in costs and high in safety, potassium that is an alkali metal remains on the substrate surface after cleaning.
Patent Document 5 describes a cleaning agent containing cysteine for cleaning a semiconductor substrate having a copper wiring given thereto after a CMP step. However, Patent Document 5 does not disclose a cleaning agent containing both an amino acid such as cysteine, etc. and an inorganic alkali. In addition, Patent Document 5 describes only results of observing corrosion of copper but does not describe a specific cleaning effect.
Patent Documents 6 and 7 disclose, as a cleaning agent of a glass substrate, a cleaning agent containing a specified anionic surfactant, an inorganic alkali, and a chelating agent. However, Patent Documents 6 and 7 do not describe that this cleaning agent was used for cleaning a semiconductor substrate after a CMP step.
Patent Document 8 discloses, as a cleaning agent for sacrificial anti-reflective material, a cleaning agent containing an alkali component, a chelating agent, and a surfactant. However, Patent Document 8 does not describe that this cleaning agent was used for cleaning a semiconductor substrate after a CMP step.
That is, it was not general to use an inorganic alkali as a substrate cleaning agent after the CMP step.